1. Technical Field
The present invention relates to an illuminating apparatus that illuminates an original, an image reading apparatus, and an image forming apparatus.
2. Related Art
Generally, in image reading apparatuses provided in image forming apparatuses such as copiers, fax machines or digital multi-functional peripherals, or image reading apparatuses connected to a computer via communication means such as a network, light reflected from an original illuminated by an illuminating apparatus including a light source is read as original image.
For example, a conventional image reading apparatus includes an illuminating apparatus in which a light source for illuminating an original placed on an original stage glass and a first mirror are arranged, second and third mirrors, an imaging lens and an image sensor (for example, a line sensor such as a CCD (Charge Coupled Device)), and many of such image reading apparatuses are configured to read an original image by causing light reflected from the original illuminated by the light source to travel via the first mirror, the second mirror, the third mirror and then the imaging lens to form an image on the image sensor.
Also, an image reading apparatus is used as an image reading means when information on an image formed on an image sensor such as a CCD is converted to electronic signals and subjected to image processing, and transferred to an image forming portion that prints the image information or sent to a computer (for example, personal computer) connected to a network, for example.
Conventionally, a bar-shaped light source such as a halogen lamp or a xenon lamp, or a light source in which a plurality of light-emitting elements such as light-emitting diodes (LEDs) are arranged in a main scanning direction may be employed as a light source provided in illuminating apparatuses.
In the case where a light source in which a plurality of light-emitting elements are arranged is employed, light-emitting elements such as LEDs have strong directional characteristics in a predetermined direction, and thus uneven illuminance corresponding to the pitch between the light-emitting elements may occur on an irradiated face of the original.
For example, as the pitch between the light-emitting elements becomes larger, uneven illuminance on the irradiated face of the original caused by repeated areas of brightness and darkness in a main scanning direction becomes more noticeable. Therefore, it is preferable to make the pitch smaller, but if the pitch is made smaller, the number of necessary light-emitting elements increases, which results in an increase in cost.
From a viewpoint of mitigating uneven illuminance described above, JP2008-118246A discloses a light irradiating apparatus in which a plurality of light-emitting elements are arranged in a zigzag manner.
Incidentally, people usually tend to recognize an irradiated face of an original on which the degree of tone of brightness and darkness is uniform as uneven illuminance. In other words, the uneven illuminance caused by repeated areas of brightness and darkness in the main scanning direction is likely to be noticeable if the amplitude and the cycle of fluctuation of the illumination distribution on the irradiated face of an original in the main scanning direction are regular.
However, in the illuminating apparatus disclosed in JP2008-118246A mentioned above, since the light-emitting elements arranged in the main scanning direction on both sides in a sub-scanning direction are arranged in a zigzag manner, the amplitude and the cycle of fluctuation of the illumination distribution in the main scanning direction on the irradiated face of an original become regular, and accordingly the uneven illuminance is likely to be noticeable.
Therefore, it is an object of the present invention to provide an illuminating apparatus including a plurality of rows of light source groups each of which has a plurality of light-emitting elements that irradiates light to an original arranged in a main scanning direction, an illuminating apparatus being capable of making, less noticeable, uneven illuminance caused by repeated areas of brightness and darkness on an irradiated face of the original in the main scanning direction, an image reading apparatus and an image forming apparatus.
Note that the references for the technique related to the present invention include JP H4-344992A. Specifically, JP H4-344992A discloses an LED unit for an image sensor, in which a plurality of LEDs are arranged in series on a plurality of wires connected in parallel. When those LEDs are arranged, if one of the LEDs on a single wire fails and is disconnected, a current does not flow through any of the other LEDs on the same wire either, and the luminance on an irradiated face of an original partially decreases. To avoid this, between the LEDs on a single wire, the LEDs on another wire are separately arranged in a row.